1. Field of the Invention
The present invention relates to a method and apparatus for processing organic chlorine compounds.
2. Related Background Art
There are cases where objects to be processed such as fly ash or main ash generated from waste incinerators, leachate from waste disposal facilities, suspended matters contained in the leachate, soils contaminated by inappropriately disposed wastes, and biological sludge subjected to leachate treatments contain a high concentration of hard-to-decompose organic chlorine compounds represented by dioxins. There are urgent social needs for eliminating or detoxifying the hard-to-decompose organic chlorine compounds. Recently, various methods for decomposing and processing materials containing such organic chlorine compounds have been proposed.
Among these methods, examples of physicochemical methods include high temperature incineration method, molten salt incineration method, active carbon adsorption method, gamma ray decomposition method, ozone decomposition method, wet type air oxidization method, catalyst incineration method, supercritical hydroxylation method, alkaline chemical decomposition method, alkaline catalyst decomposition method, thermal desorption method, and the like. On the other hand, as a biological method, Japanese Patent Application Laid-Open No. HEI 10-323646 and Japanese Patent Application Laid-Open No. HEI 10-257895 disclose methods using microorganisms having a lignin decomposing capability.
Also, literatures, e.g., Hiroyuki Nakagawa et al., xe2x80x9cBio-Remediation of Environment Contaminated with Aromatic Compounds,xe2x80x9d Water Purification and Liquid Wastes Treatment, 39, 535-544 (1998), pp.539-540; Satoshi Takada, xe2x80x9cPossibility of Decomposition of Dioxins by White-Rot Fungus,xe2x80x9d the 23rd Lecture Meeting of Japan Society for Environmental Chemistry, Advanced Abstracts, 35-40 (1998); Tomohiko Ishiguro, xe2x80x9cDecomposition and Elimination of Noxious Chemical Materials Such as Dioxins by Microorganisms,xe2x80x9d Journal of Water and Waste, 33, 645-651 (1991); and the like generally describe methods using polychlorinated biphenyl (PCB) decomposing microorganisms, white-rot fungus, and the like. Further, a literaturexe2x80x94C. Klimm et al., Chemosphere, 37, 2003-2011 (1998)xe2x80x94reports an example of processing dioxins in a case where an object to be treated is kept under an anaerobic condition.
The inventors have studied the above-mentioned conventional methods and, as a result, have found the following problems. Namely:
(1) Conventional physicochemical methods often necessitate complicated, large-scale apparatus for fully decomposing organic chlorine compounds, such as dioxins, contained in the object to be processed. Among them, there are methods for which high temperature, high pressure, and the like are indispensable conditions. Therefore, if such methods are employed, then the processing tends to take time and labor, thereby raising the processing cost.
(2) Microorganisms employed in conventional biological methods tend to be hard to handle and collect. Also, there is a tendency that the kinds of dioxins fully decomposable thereby are limited, and the processing with a favorable stability and reproducibility is hard to carry out. As a result, the efficiency of decomposing dioxins may not always be sufficient.
(3) In the method in which the object to be processed is kept under an anaerobic condition, the effect of reducing dioxins with time cannot fully be obtained.
In view of such circumstances, it is an object of the present invention to provide a method and apparatus for processing organic chlorine compounds, which can decompose hard-to-decompose organic chlorine compounds such as dioxins by a treatment simpler than conventional ones, can remarkably improve the efficiency of decomposition, and can lower the processing cost.
For solving the above-mentioned problems, the inventors have repeated diligent studies, and have found that, if a specific microorganic body is caused to act on an object to be processed containing an organic chlorine compound such as a dioxin under a predetermined condition, the organic chlorine compound can be decomposed. Also, the inventors have found that the decomposing rate of organic chlorine compound can be enhanced if components inhibiting the decomposition of organic chlorine compound by the microorganic body are eliminated under a predetermined processing condition. The inventors have further repeated studies based on these findings, thereby accomplishing the present invention.
Namely, the method of processing an organic chlorine compound in accordance with the present invention is a method of decomposing and eliminating the organic chlorine compound in an object to be processed, the method comprising a biological treatment process of causing a first microorganic body capable of oxidizing reduced nitrogen to come into contact with the object to be processed, and biologically processing the object to be processed in a state containing the first microorganic body, so as to decompose the organic chlorine compound.
In such a method of processing an organic chlorine compound, if an aerobic treatment is carried out as the biological treatment, then a nitrifying reaction in which reduced nitrogen is oxidized by the first microorganic body is carried out. At this time, along with the nitrifying reaction, a reaction of decomposing the organic chlorine compound contained in the object to be processed proceeds, whereby the organic chlorine compound is decomposed, so as to turn into lower hydrocarbon, carbon dioxide, water, and the like.
Though the mechanism of decomposing the organic chlorine compound has not fully been elucidated, it is presumed that a conjugate reaction such as co-oxidation, for example, proceeds in an enzymatic reaction system in which an oxidase produced by the microorganic body involves, whereby the organic chlorine compound is oxidized and decomposed along with the oxidization (nitrification) of reduced nitrogen. However, the action is not restricted thereto. Such an enzymatic reaction does not necessitate severe reaction conditions such as high temperature and high pressure in particular, whereby hard-to-decompose organic chlorine compounds can be decomposed by very simple processing.
Preferably, a reduced nitrogen adding process for adding reduced nitrogen to the object to be processed is provided. As a consequence, an amount of reduced nitrogen sufficient for carrying out the aerobic treatment as the biological treatment can be supplied. Hence, the reaction of oxidizing reduced nitrogen by the first microorganic body and, consequently, the reaction of decomposing the organic chlorine compound can be caused to proceed reliably and sufficiently.
Thus, it is preferred that the biological treatment process comprises an aerobic treatment process of oxidizing reduced nitrogen contained in the object to be processed with the first microorganic body and decomposing the organic chlorine compound in an aerobic atmosphere. Here, as the first microorganic body, nitrite bacteria, nitrate bacteria, and the like which are easy to obtain and culture are preferably used. Examples of reduced nitrogen are those oxidized by such a first microorganic body, such as ammonium ion and urea, which may be originally contained in the object to be processed or be added thereto.
If the anaerobic treatment is carried out as the biological treatment, then the activity of first microorganic body for oxidizing reduced nitrogen tends to decrease. However, it has been verified that the organic chlorine compound in the object to be processed is favorably decomposed even in an anaerobic atmosphere in the state where the biological activity of the first microorganic body is maintained by way of a biologic treatment in an aerobic atmosphere (which may be the above-mentioned aerobic treatment process).
Though details of the mechanism of decomposing the organic chlorine compound have not been clear, it is presumed that, for example, an oxidase produced by the first microorganic body in the aerobic treatment is eluted as the first microorganic body is disassembled under the anaerobic condition, whereby the organic chlorine compound is oxidized and decomposed by an enzymatic reaction in which this oxidase involves. However, the action is not restricted thereto. As mentioned above, since such an enzymatic reaction does not necessitate severe reaction conditions such as high temperature and high pressure in particular, hard-to-decompose organic chlorine compounds can be decomposed by a very simple processing.
Thus, it will also be preferable if the biological treatment process comprises an anaerobic treatment process in which the object to be processed containing the first microorganic body keeping its biological activity by way of a biological treatment in an aerobic atmosphere is held in an anaerobic atmosphere. In addition, it is desirable that, in this anaerobic treatment process, supply of a gas including oxygen to the object to be processed is blocked, so as to form an anaerobic atmosphere, and this anaerobic atmosphere is maintained. In the anaerobic treatment process, it will be further preferable if the temperature of the object to be processed is held at 15xc2x0 C. or higher, since the reaction of decomposing the organic chlorine compound is remarkably accelerated thereby.
It will be further preferred if the method further comprises an oxidized nitrogen eliminating process of reducing and eliminating oxidized nitrogen contained in the object to be processed with a second microorganic body capable of reducing oxidized nitrogen in an anaerobic atmosphere. If the object to be processed is one subjected to a nitrogen treatment of leachate or one with which the above-mentioned aerobic treatment process is carried out, for example, then oxidized nitrogen such as nitrate ion and nitrite ion generated upon oxidization of reduced nitrogen by the first microorganic body is contained in the object to be processed. Also, some of objects to be processed originally contain oxidized nitrogen. For such oxidized nitrogen, an environmental emission standard value has been defined, and there is a fear that the purified water or purified product obtained by processing the object to be processed may contain oxidized nitrogen by a nitrogen content exceeding its standard value in some cases.
The inventors have also found that the decomposing efficiency of inorganic chlorine compound in the aerobic and anaerobic treatment processes decreases if such oxidized nitrogen exists in the object to be processed. In the anaerobic treatment process in particular, the organic chlorine compound tends to be insufficiently eliminated if the object to be processed contains a microorganic body, such as denitrifying bacteria, adapted to reduce oxidized nitrogen as in the case of biological sludge subjected to a biological treatment. It is presumed that, if oxidized nitrogen exists under an anaerobic condition, then the activity of the denitrifying bacteria is maintained and, under the influence thereof, the first microorganic body is restrained from being disassembled, whereby the elution of oxidase is stagnated. However, the action is not restricted thereto.
If the object to be processed containing such oxidized nitrogen is subjected to the oxidized nitrogen eliminating process, then a denitrifying reaction in which the second microorganic body reduces oxidized nitrogen by using oxidized nitrogen and nutrients is carried out. As a consequence, oxidized nitrogen can be eliminated under a mild condition of normal temperature and normal pressure by turning it into nitrogen, carbon dioxide, water, and the like. As a consequence, the decomposing efficiency of organic chlorine compound in the aerobic and anaerobic treatment processes can fully be prevented from decreasing. Here, denitrifying bacteria and the like which are easy to obtain and culture are preferably used as the second microorganic body. Preferably, the oxidized nitrogen eliminating process is carried out before the aerobic treatment process, after the aerobic treatment process, or before the anaerobic treatment process.
More preferably, the aerobic treatment process has a first microorganic body adding step of adding the first microorganic body to the object to be processed; a reduced nitrogen adding step of adding reduced nitrogen to the object to be processed; and a decomposing step of supplying a gas containing oxygen to the object to be processed, so as to form an aerobic atmosphere, and causing the first microorganic body to oxidize reduced nitrogen and decompose the organic chlorine compound.
If the object to be processed is one containing a sufficient amount of the first microorganic body and/or reduced nitrogen beforehand, as with sludge generated upon another biological treatment, for example, then the first microorganic body adding step and/or reduced nitrogen adding step may not be carried out. Also, the first microorganic body adding step and reduced nitrogen adding step may be carried out simultaneously, or any of them may be carried out earlier, whereas they can be carried out before or simultaneously with the decomposing step. Here, the reduced nitrogen adding step is substantially equivalent to the above-mentioned reduced nitrogen adding process.
In this manner, oxygen is supplied to the object to be processed, so that an aerobic atmosphere is formed favorably, whereby a nitrifying reaction in which the first microorganic body oxidizes reduced nitrogen and its accompanying reaction of decomposing organic chlorine compound proceed under a mild condition of normal temperature and normal pressure. As a consequence, hard-to-decompose organic chlorine compounds can be decomposed by a mild and simple treatment at normal temperature and normal pressure without necessitating severe reaction conditions such as high temperature and high pressure. Also, since reduced nitrogen is positively added, the nitrifying reaction caused by the first microorganic body can be maintained favorably.
More preferably, the oxidized nitrogen eliminating process has a second microorganic body adding step of adding the second microorganic body to the object to be processed; a carbon source adding step of adding to the object to be processed an organic carbon source which becomes a nutrient for the second microorganic body; and an eliminating step of blocking supply of a gas containing oxygen to the object to be processed, so as to form an anaerobic atmosphere, and causing the second microorganic body to reduce and eliminate oxidized nitrogen.
If the object to be processed is one containing a sufficient amount of the second microorganic body and/or organic carbon source beforehand, such as surplus sludge generated upon another biological treatment, then the second microorganic body adding step and/or carbon source adding step may not be carried out. Also, the second microorganic body adding step and carbon source adding step may be carried out simultaneously, or any of them may be carried out earlier, whereas they can be carried out before or simultaneously with the eliminating step. If such an oxidized nitrogen eliminating step is carried out, then the second microorganic body grows while using the organic carbon source (also referred to as carbon source or hydrogen donor) as a nutrient, during which a denitrifying reaction for reducing oxidized nitrogen is favorably carried out.
It will also be preferred if an object to be processed mixing process of adding to and mixing with the object to be processed in at least one of the aerobic treatment process, oxidized nitrogen eliminating process, and anaerobic treatment process another object to be processed, different therefrom, containing an organic chlorine compound. In this manner, the other object to be processed can be processed by use of the first microorganic body acclimatized to the environment of use in each process. As a consequence, the decomposing efficiency of the organic chlorine compound contained in the other object to be processed is enhanced.
More preferably, as the first microorganic body and/or second microorganic body, those in a dehydrated cake form whose moisture is at least partly eliminated or in a lyophilized powder form are used.
Microorganic bodies are often obtained in the form of biological sludge as being cultured and acclimatized in a liquid such as a culture liquid in general. If a dehydrated cake form of biological sludge whose moisture is at least partly eliminated is used as a microorganic body, then its volume can be lowered. Also, since it is not liquid, its handling such as transportation and storage and operations for adding it to the object to be processed become easier, and the space for its storage and stock can be reduced. Further, since the moisture necessary for growing microorganic bodies decreases, the growth of inutile microorganic bodies which carry out no nitrifying reaction or inhibit the nitrifying reaction is suppressed.
On the other hand, if microorganic bodies are in a lyophilized powder form, then their volume reduction ratio is high, their volume can further be lowered, handling upon transport and storage as well as operations of adding them to the object to be processed become further easier, and the space for storage and stock can further be reduced. Also, since the moisture is eliminated by lyophilization, the above-mentioned growth of inutile microorganic bodies is further suppressed. Further, long-term storage is facilitated.
It will be useful if the method comprises a slurry-forming process of causing at least one of the object to be processed, the first microorganic body, and the second microorganic body to become slurry. In this manner, even if the object to be processed is a solid having a low water content, such as fly ash or soil, for example, the object to be processed can be made easier to flow. As a consequence, it becomes easier to supply a gas including oxygen to the object to be processed, whereby an aerobic atmosphere is further favorably formed.
As a result, the nitrifying reaction caused by microorganic bodies becomes active, whereby the reaction decomposing of organic chlorine compound accompanying the nitrifying reaction is accelerated. Also, it becomes easier for the first microorganic body and the oxidase produced by the first microorganic body to come into contact with the organic chlorine compound. Therefore, the nitrifying reaction caused by the first microorganic body and its accompanying reaction of oxidizing and decomposing the organic chlorine compound are further accelerated. Further, it becomes easier for the second microorganic body and oxidized nitrogen to come into contact with each other, whereby the reaction of decomposing oxidized nitrogen is accelerated. Also, when the first microorganic body and/or second microorganic body is used in the form of dehydrated cake or powder, their fluidity increases, whereby their miscibility with the object to be processed improves. As a result, the decomposing efficiency of organic chlorine compound can further be improved.
It will further be preferred if the aerobic treatment process has a pH adjusting step of adjusting the pH of the object to be processed containing the first microorganic body and reduced nitrogen to a range of 5 to 9, and/or a desalting step of adjusting the salt concentration of the object to be processed to 4% or lower. If such a pH condition is attained, the growth of first microorganic body becomes active, and its activity can be kept high. Therefore, the nitrifying reaction caused by the first microorganic body and its accompanying reaction of decomposing the organic chlorine compound can improve their efficiency.
If the salt concentration of the object to be processed exceeds 4%, then the activity of oxidase produced by the first microorganic body tends to be suppressed, whereby it becomes harder to maintain the nitrifying reaction. As a result, the nitrifying reaction is stagnated, whereby the reaction of decomposing the organic chlorine compound, in which this oxidase is supposed to be involved, tends to be suppressed. Here, if the salt concentration of the object to be processed prior to the addition of the first microorganic body and reduced nitrogen is 4% or lower, then the salt concentration in the object to be processed in a later treatment can reliably become 4% or lower.
In addition, it is desirable that, in the reduced nitrogen adding process and/or reduced nitrogen adding step, reduced nitrogen be added to the object to be processed such that the content of reduced nitrogen with respect to 1 ng of the organic chlorine compound becomes 0.01 to 10.0 g-N. If this adding ratio is less than 0.01 g-N, then the amount of nitrifying reaction becomes insufficient, whereby the reaction of decomposing the organic chlorine compound would not proceed sufficiently. If the adding ratio exceeds 10.0 g-N, by contrast, then the nitrifying reaction remarkably lowers the pH in the object to be processed. As a result, the amount of alkali agent injected for adjusting the pH increases, which is uneconomical. Also, there is a fear that the pH adjustment may raise the salt concentration and inhibit the nitrifying reaction. Here, the unit xe2x80x9cg-Nxe2x80x9d indicates that it is the weight of nitrogen.
The apparatus for processing an organic chlorine compound in accordance with the present invention is aimed at effectively carrying out the method of processing the organic chlorine compound in accordance with the present invention, which is an apparatus for decomposing and eliminating the organic chlorine compound in an object to be processed, the apparatus comprising a biological treatment section in which a first microorganic body capable of oxidizing reduced nitrogen and the object to be processed come into contact with each other, and the object to be processed in a state containing the first microorganic body is biologically processed, so as to decompose the organic chlorine compound. Here, it will be preferable if a reduced nitrogen adding section for adding reduced nitrogen to the object to be processed is further provided.
Further, it is preferred that the biological treatment section comprises an aerobic treatment section, formed with an aerobic atmosphere, in which reduced nitrogen contained in the object to be processed is oxidized by the first microorganic body, and the organic chlorine compound is decomposed; and/or an anaerobic treatment section, formed with an anaerobic atmosphere, for holding in the anaerobic atmosphere the object to be processed containing the first microorganic body keeping a biological activity by way of a biological treatment in an aerobic atmosphere.
More preferably, in the anaerobic treatment section, the object to be processed is supplied, supply of a gas containing oxygen to the object to be processed is blocked, so as to form an anaerobic atmosphere, and this anaerobic atmosphere is maintained. Further, it will be useful if the anaerobic treatment section has a temperature adjustment section capable of adjusting the temperature of the object to be processed.
It is desirable that an oxidized nitrogen eliminating section in which oxidized nitrogen contained in the object to be processed is reduced and eliminated by a second microorganic body capable of reducing this oxidized nitrogen be further provided.
Specifically, it is further preferred that the aerobic treatment section comprises a first microorganic body adding section for adding the first microorganic body to the object to be processed; a reduced nitrogen adding section for adding reduced nitrogen to the object to be processed; a diffuser section for sending a gas containing oxygen to the object to be processed; and a first reaction treatment section in which the object to be processed is supplied, and the first microorganic body oxidizes reduced nitrogen and decomposes the organic chlorine compound.
It is also preferred that the oxidized nitrogen eliminating section have a second microorganic body adding section for adding a second microorganic body to the object to be processed; a carbon source adding section for adding to the object to be processed an organic carbon source which becomes a nutrient for the second microorganic body; and an eliminating section in which the object to be processed is supplied, supply of a gas containing oxygen to the object to be processed is blocked, and oxidized nitrogen is reduced and eliminated by the second microorganic body.
Further, it is preferred that an object to be processed mixing section for adding to and mixing with the object to be processed in at least one of the aerobic treatment section, oxidized nitrogen eliminating section, and anaerobic treatment section another object to be processed, different therefrom, containing an organic chlorine compound be provided.
It is further preferred that a slurry-forming section in which a liquid is added to and mixed with at least one of the object to be processed, first microorganic body, and second microorganic body, so as to cause at least one of the object to be processed, first microorganic body, and second microorganic body to become slurry be provided. In addition, it is further preferred that the aerobic treatment section have a pH adjustment section for adjusting the pH of the object to be processed containing the first microorganic body and reduced nitrogen, and/or a desalting section for adjusting the salt concentration of the object to be processed.
In the present invention, dioxins refer to at least one kind of or a mixture of at least two kinds (including homologues) of polychlorinated dibenzoparadioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and coplanar polychlorinated biphenyls (coplanar PCBs).
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.